1. Field of the Invention
The present invention relates to a deposition apparatus and an etching apparatus, which employ microwave plasma or a radio frequency (RF) plasma and, more particularly, to a deposition apparatus and an etching apparatus, which can minimize damage to a microwave or RF entrance window and maintain the stability of a plasma by locating the plasma away from the entrance window.
2. Related Background Art
Microwave plasma or radio frequency plasma (RF plasma) is used to regulate and enhance a plasma in depositing or etching processes such as plasma CVD or plasma etching, for the purpose of increasing the processing efficiency. For example, microwave CVD or RF plasma CVD is often used for the vapor-phase synthesis of diamond. Vapor-phase synthesis of diamond for which microwave CVD or RF plasma CVD is usable will be described below from the viewpoint of its applicability.
Diamond is a useful material for cutting and polishing tools because of its excellent hardness, wear resistance, and thermal conductivity. In addition, wide electrical and optical applications are expected because diamond has a wide band gap, a high resistance to radiation, and optical transparency for wide range of from infrared to ultraviolet. In particular, to apply diamond with importance being placed on its optical or electrical properties, a diamond film with a large area and high quality must be obtained by controlling inclusion of impurities.
Methods for synthesizing diamond can be generally classified into high-pressure synthesis and vapor-phase synthesis. In particular, vapor-phase synthesis is superior in controlling a large area and impurities. Conventionally, various vapor-phase synthesis methods have been examined to synthesize diamond, including filament CVD, microwave plasma CVD, radio frequency plasma (RF plasma) CVD, a plasma jet method, and a combustion flame method. Of the synthesis methods above, microwave plasma CVD and RF plasma CVD are suitable for synthesis of high-purity diamond. Otherwise, inclusion of impurities poses a problem. For example, metal contamination is caused by a filament in filament CVD, or by an electrode in the plasma jet method. In the combustion flame method, nitrogen in air can hardly be prevented from being contained in diamond.
As described above, microwave plasma CVD and RF plasma CVD are superior in terms of the purity of resultant diamond is concerned, while it is difficult to obtain large area, high-density homogeneous plasma for large-area processing. Additionally, in these apparatuses, a window for guiding a microwave or an RF wave is heated by the plasma, so that the service life of the window or foreign substance generation is adversely influenced. Furthermore, the window is inevitably sputtered by the plasma.
Attempts for the improvement in guiding microwave into processing apparatus are disclosed in the art. For example, in Japanese Patent Publication No. 7-54757, the shape of a microwave antenna and the vacuum seal portion of a window are implemented to prevent the vacuum seal portion from being collided and damaged by the generated plasma. In this attempt, however, the entire window is inevitably sputtered by the plasma.
In Japanese Patent Publication No. 7-54758, a horn-shaped antenna is used to spread the plasma over the desired area. However, the effect of the apparatus disclosed in Japanese Patent Publication No. 7-54758 is obtained only in the case where a magnetic field is applied within a high-vacuum state at 1.times.10.sup.-3 Torr, as described in the embodiments, which does not meet the typical diamond synthesis conditions.
In Japanese Patent Publication No. 7-54759, an efficient microwave introduction method is discussed in association with mode selection in microwave introduction regarding an applied magnetic field. However, this prior art examines only in a low-pressure plasma to which applying magnetic field is effective. No examination is made for the window for guiding a microwave, so solving the problem of the entrance window is not addressed.
In Japanese Patent Publication No. 7-11995, the gas supply method is implemented, and a discharge chamber is arranged near the antenna, thereby homogenizing the gas.
However, this apparatus can hardly efficiently generate a plasma in a reaction chamber at a pressure suitable for diamond synthesis, i.e., at a high pressure of, e.g., 1 Torr or more. This is because, at a relatively high pressure for obtaining a high-density plasma, the plasma generated near the microwave entrance window does not spread to a substrate. In addition, at a high pressure, the mean free path of charged particles becomes shorter than that at a low pressure, though plasma control using a magnetic field becomes more difficult than that at a low pressure. For this reason, the microwave entrance window is inevitably heated and sputtered by the plasma. Furthermore, since the plasma distribution is non-uniform because of the non-uniformity of the electric field of the microwave, heterogeneity of the diamond film cannot be avoided.
In particular, when a plasma is generated at a high pressure of 1 Torr or more, the plasma is also excited near the microwave entrance window, so the plasma cannot be stably maintained. The microwave entrance window on which the atmospheric pressure acts is heated and damaged.
Japanese Patent Application Laid-Open No. 5-166596 discloses an attempt to solve the above mentioned problem on microwave entrance window, in which a microwave processing apparatus is provided with a slit at downstream side from a microwave entrance window of a waveguide to decrease pressure around the microwave entrance window. In this apparatus, plasma generation is inhibited around the window because of the lower pressure, so that the damage of the entrance window is avoided. Japanese Patent Application Laid-Open No. 6-275566 also discloses another attempt to solve the above mentioned problem, in which plurality of partition plates is disposed in a microwave plasma processing apparatus, where the partition plates is positioned at a location relatively far from the substrate holder, thereby reducing damage of substrate.
However, these attempts do not address to the case where higher microwave power is required for processing, e.g., deposition of diamond materials. In such case, higher microwave power cause the local temperature elevation in plasma, thereby damaging microwave entrance window. When synthesis is performed at a low temperature in such conventional apparatus, the substrate is subjected to microwave, and is inductively heated by the microwave. Further, in the conventional apparatuses, a diamond film thickness distribution is formed even on a flat substrate. The conventional apparatuses cannot be applicable to substrates having three-dimensional shape.